each of the songs in 生きる / ikiru / alive have a specific theme has listed in songs that have PVs and in UMAA’s blog post about ikiru
original quote from blog post:
本作の収録曲には1曲目より、「誕生」「成長」「衝動」「葛藤」「栄光」「決意」「旅立」「孤独」「変化」「今」「明日」「未来」「人生」という順序で各曲にサブテーマが込められている、まさに人生における酸いも甘いも体感することの出来る作品である。
machine translated:
Each song in this album has a sub-theme in the order of "birth," "growth," "impulse," "conflict," "glory," "determination," "departure," "loneliness," "change," "now," "tomorrow," "future," and "life," allowing the viewer to experience both the sweet and sour aspects of life.